An image sensor is a device including several million elements for transforming light to an electrical signal, depending upon the intensity of radiation received by the device. The image sensor can be installed in a digital input device, which enables recording of pre-digitalized images to digitalized images. Recently, the need for these devices has remarkably increased for use in various security devices and digital porters.
The image sensor includes a pixel array, which is a plurality of pixels arranged in a two-dimensional matrix format. Each pixel includes photosensitive means and transmission and signal output devices. Depending upon the transmission and signal output devices, the image sensor is broadly classified into two kinds: a charge coupled device (CCD) type of image sensor and a complementary metal oxide semiconductor (CMOS) type of image sensor.
FIG. 4 illustrates a CMOS image sensor 100 to explain the role of a color filter in the image sensor. As an example, incoming light reaches a color filter 5 through a microlens 1 and a second overcoating layer (OCL) 3, and is separated into each of R, G, and B in the color filter 5. Then, the color filter transmits the light through a first overcoating layer (OCL) 7, a passivation layer 9, and an inter-metal dielectric layer (IMD) 11, and then to a photodiode 13 corresponding to each pixel formed on an interlayer dielectric layer (ILD) 15.
Photosensitive resin compositions for a liquid crystal display (LCD) color filter that are developed in an alkali aqueous solution developer have been actively studied. As the unit pixel is decreased in size from the conventional size of 5 to 3 μm to 1 μm or less to improve image quality of digital cameras, however, there is a need for improved photosensitive resin compositions.
For example, as the unit pixel is decreased in size to 1 μm or less, it is necessary to consider the geometric optic and wave optic aspects in relation to the microlens since the size of the unit pixel can be up to about 1.5 times the visible ray wavelength range.
More specifically, as the unit pixel is decreased in size, the diameter of each microlens is decreased. Therefore, unless the focal distance of each lens is decreased, the resolution is deteriorated by the crosstalk phenomenon between adjacent pixels. In order to solve these problems, an overcoating layer can be eliminated from the lower layer of the color filter to decrease the distance between the microlens and the photodiode, and the color filter can be formed on a passivation layer (SiNx). Alternatively, the color filter may be formed on an inter-metal insulation layer from which the passivation layer is eliminated.
In this case, each RGB pixel deteriorates the pattern residues and resolution characteristics, unlike the case of manufacturing it on the conventional overcoating layer.
A device and method for an image sensor color filter are disclosed in Korean Patent Laid-Open Publication No. 2002-039125, Japanese Patent Laid-Open Publication Pyong 10-066094, Korean Patent Laid-Open Publication No. 1998-056215, Japanese Patent Laid-Open Publication Pyong 7-235655, Korean Patent Laid-Open Publication No. 2003-056596, Japanese Patent Laid-Open Publication No. 2005-278213, Korean Patent Laid-Open Publication No. 2003-002899, and Japanese Patent Laid-Open Publication Pyong 11-354763; and an image sensor color filter composition is disclosed in Korean Patent Laid-Open Publication No. 2006-0052171, Japanese Patent Laid-Open Publication No. 2004-341121, and Japanese Patent Laid-Open Publication Pyong 7-172032. Korean Patent Laid-Open Publication No. 2006-0052171 and Japanese Patent Laid-Open Publication No. 2004-341121 disclose a polymer having a double bond with a dye in order to provide a pixel having a high density, so that a 2.0×2.0 μm fine pattern may be provided. However, because the method uses a dye instead of a pigment as a colorant, there can be problems with regard to long-term reliability due to weak dye photo resistance and heat resistance. Furthermore, in Japanese Patent Laid-Open Publication Pyong 7-172032, a black matrix is introduced in order to prevent color mixing and seceding between each of R, G, and B pixels. However, this method needs an additional step to provide the black matrix, and it is substantially impossible to provide a black matrix having the required fine size. It also has a drawback of decreasing the aperture ratio due to introducing the black matrix.